Recently, by addressing global environmental issues such as a global warming issue and a global energy issue, a hybrid vehicle and an electric vehicle have become popular in an automotive field, and a number of home electrical appliances having an inverter motor drive are increased due to an energy-saving solution. In the fields of hybrid vehicle, electric vehicle, and inverter motor drive, it is important to use a power semiconductor device which converts DC into AC or vice versa, or transforms a voltage.
However, a silicon (Si) used as a power semiconductor device for a long time is about to reach a performance limitation, thereby hardly expecting a dramatic performance improvement. A next-generation power semiconductor device has been therefore focused on that comprises a material such as silicon carbide (SiC), gallium nitride (GaN), and diamond.
SiC and GaN have advantageous properties such that their band gaps are approximately three times larger and their insulation breakdown field strengths are more than ten times larger, compared with the properties of Si. Further, SiC and GaN have other advantageous properties such as high operating temperature (a report exists about SiC operating in 650° C.), high thermal conductivity (SiC is as almost same as Cu), and large saturation electron drift velocity. Due to the properties described above, it is possible to decrease an on-resistance of a power semiconductor device and dramatically reduce power loss of a power converter circuit.
Currently, a power semiconductor device is generally protected by a transfer molding with epoxy resin, a potting sealing with silicone gel, or the like. Particularly, in an automobile field, the transfer molding with epoxy resin is about to become a mainstream in view of reduction in size and weight of a power semiconductor. An epoxy resin is a heat-curable resin, and excellent in moldability, adhesion with base material, and mechanical strength, thereby being a well-balanced material. However, thermodecomposition of a cross-linked point in an epoxy resin progresses in a temperature over 200° C. Therefore, it is possible not to use an epoxy resin as a sealant in a high temperature operation where SiC and GaN are expected to be used.
For achieving this expectation, a cured product of a cyanic acid ester compound has been studied, which has over 200° C. heat resistance. This cured product of a cyanic acid ester compound can be obtained by using a catalyst which accelerates a curing process because a cyanic acid ester compound generally does not progress a heat curing reaction (trimerization reaction) in a low temperature (see, references 1 to 3, for example).